1. Field of the Invention
The present invention relates to a hub for a disk type recording medium such as an optical disk, an optical-magnetic disk, a floppy disk, a cleaning disk or the like.
2. Discussion of Background
There have been known optical disks, optical-magnetic disks, floppy disks and other disks as disk type recording media for recording information such as sounds, voices, pictures and data. There have also been known disks for cleaning a head for a driving unit on which a floppy disk is mounted. Some types of the disk type recording medium are provided with a hub at its center. There are two types of hub for a disk type recording medium, i.e. one being formed by drawing a single metallic circular plate to form a flange portion at its outer periphery and the other being formed by a metallic portion and a resinous portion in one-piece body. The later is more advantageous than the former because it has good machining accuracy, it is manufactured at a low cost and processability to attach a hub to the disk is high.
For instance, a hub to be attached to an optical disk cartridge has a construction as shown in FIG. 16, (a plane view) and FIG. 17 (a cross-sectional view taken along a line A--A in FIG. 16). In FIGS. 16 and 17, a reference numeral 10 designates a flat circular plate which constitutes a metallic part, and a numeral 12 designates a resinous part. A plurality of openings 14, which are used for fixing the resinous part, are formed vertically near the outer circumferential portion of the metallic part 10. When insertion-molding of a resinous material is carried out, the resinous material is filled in the openings 14 and cured there, whereby the resinous part 10 is firmly attached to the metallic part 10. A reference shaft insertion hole 16 is formed at the center of the metallic part 10, and an annular projection 18 is formed by melt-bonding near the outer periphery of the resinous part 12 so as to be able to attach a disk at the lower face. A bonding means such as an adhesive agent or an adhesive tape may be provided instead of the annular projection 18. The reference shaft insertion hole 16 functions as a standard to determine a position of the disk to a driving unit.
A construction of another conventional hub used for an optical disk cartridge is shown in FIG. 18 (a plane view) and FIG. 19 (a cross-sectional view taken along a line B--B in FIG. 18). In FIGS. 18 and 19, a reference numeral 20 designates a flat circular plate which constitutes a metallic part, and a numeral 22 designates a resinous prat. A plurality of projections 24 are formed at the outer periphery of the metallic part 20 so as to be inclined. When insertion-molding of a resinous material is carried out, the resinous material surrounds around the projections 24, whereby the resinous part 22 is firmly fixed to the metallic part 20. A reference shaft insertion hole 26 is formed at the center of the metallic part 20.
However, the hub illustrated in FIGS. 16 and 17 in which the holes 14 for fixing the resinous part to the metallic part is formed vertically near the outer circumference of the metallic part 10 requires means for preventing the resinous part from coming off. Namely, it is necessary to form a tapered portion or an undercut portion in the inner wall surface of the holes. However, it is difficult to provide such measures around the outer circumference by a stamping operation. Since a strain is apt to take place when a large opening is formed, it is difficult to obtain a sufficient strength at an area having a large hole. Further, the resinous part is apt to separate from the metallic part when the holes are formed near the reference shaft insertion hole.
In the hub illustrated in FIGS. 18 and 19 in which the projections 24 are formed at the outer periphery of the metallic part 20 so as to be inclined from the flat surface of the metallic part 20, the outer configuration is inevitably large because of the presence of the projections 24, whereby manufacturing cost becomes high. Further, since a very thin resinous part has to be formed, there sometimes causes a short shot 30 as shown in FIG. 20 wherein a molten resinous material does not flow in a very thin gap in the mold at the time of the insertion-molding. When such short shot takes place, plainness in the surface of the hub is deteriorated to thereby provide a poor appearance.